Gas turbine engines comprise a compressor section, a combustor section and a turbine section. Each of these sections comprises an inlet end and an outlet end, and intervening components may connect these sections. A combustor transition member, commonly referred to as a transition (and also referred to as a “transition duct” or “tail pipe” by some in the art) is mechanically coupled between the combustor section outlet end and the turbine section inlet end to direct a working gas from the combustor section into the turbine section. Conventional transitions may be of the solid wall type or interior cooling channel wall type, and the type with interior cooling channels includes those in which cooling air passes from the exterior to the interior (open-type cooling) and those in which cooling air does not enter the transition interior (closed-type cooling).
The working gas is produced by combusting an air/fuel mixture. A supply of compressed air, originating from the compressor section, is mixed with a fuel supply to create a combustible air/fuel mixture. The air/fuel mixture is combusted in the combustor to produce the high temperature and high pressure working gas. The working gas is ejected into the combustor transition member to change the working gas flow exiting the combustor from a generally cylindrical flow to a generally annular flow which is, in turn, directed into the first stage of the turbine section.
As those skilled in the art are aware, the maximum power output of a gas turbine is achieved by heating the gas flowing through the combustion section to as high a temperature as is feasible. The hot working gas, however, may produce combustor section, transition, and turbine section component metal temperatures that exceed the maximum operating rating of the alloys from which the combustor section and turbine section are made. This, in turn, may induce premature stress and cracking along various components, such as a transition. Additionally, it is appreciated that a balancing of performance and emissions is required under current environmental regulations. As to that balancing, any developments that improve both overall operational performance and overall emissions quality at reasonable cost would represent an advance in the art.
Generally, transition cooling may be effectuated fully or partially by any of the following known approaches, which represents a non-exclusive list: closed circuit steam cooling (i.e., see for one example U.S. Pat. No. 5,906,093); open cooling (in which a portion of the compressed air passes through channels in the transition and then enters the flow of combusted gases within the transition, see for one example U.S. Pat. No. 3,652,181); convection cooling (see for one example U.S. Pat. No. 4,903,477); effusion cooling (i.e., conveying air from outside the transition through angled holes into the transition); and impingement cooling (where air is directed at the transition exterior walls through apertures positioned on plates or other structures close to these walls, see U.S. Pat. No. 4,719,748 for one example). It also is noted that some of these approaches may be used in combination with one another. For example, one part of a transition may be cooled by impingement cooling, and a second part of the same transition may be cooled by a convection cooling approach.
Notwithstanding the features of current cooling approaches, when compressor air is desired to cool the transition, there is a need for appropriately designed transition cooling that additionally may benefit emissions by replacing open cooling systems. As disclosed in the following sections, the present invention provides a transition with a cooling system that is effective to achieve improved levels of cooling efficiency and may eliminate a need for open cooling systems. That is, the present invention advances the art by solving the potentially conflicting issues of cooling of transitions, conservation of fluid flow to the combustion chambers, and combustion efficiency in the transition.